A wheeled farm implement is typically connected to a tractor by a hitch which is fixed to the wheeled farm implement. One such type of wheeled farm implement can be a seed hopper or so-called "cart" for containing and supplying seeds to an air-seeder distribution system.
Such a wheeled seed-hopper implement conventionally has mounted, onto the backside thereof, an elongated frame onto which a plurality of soil-engaging ground-tool implements can be mounted. Conventional frames of this type can possess a length dimension which may be as much as two to three times as long as the distance between the seed-hopper implement wheels. Frames of this type are pulled behind the seed-hopper implement, and are generally disposed parallel to the axle connecting the centers of the seed-hopper implement wheels. Typically, the plurality of ground-tool implements are mounted on the frame, along the entire length thereof, at suitably spaced locations, and are disposed away from the wheeled farm implement. For example, when the ground-tool implement is a disc-opener and press-wheel assembly, i.e. a so-called "row unit", conventional frames may typically carry about 40-56 row units of this sort, spaced at suitable intervals along the entire length of the frame.
Conventional wheeled farm implements further generally include means for lowering and raising the frame, relative to the ground, for respectively bringing the ground tools into engagement with the ground and for raising the ground tools above the ground for transport. Such transport includes transport through the field from one work area to another, and transport to return the wheeled implement to the barn or suitable storage site. When the ground-tool implement is the disc-opener and press-wheel assembly mentioned above, it is desirable that the lowering of the frame toward the ground, into the so-called "working position", cause the disc and press wheel to come into predetermined engagement with the soil. That is, it is desirable that the disc-opener open the soil, thereby forming a seed-implanting furrow, so that the press wheel can subsequently cover a seed implanted in the furrow with moist soil. Such soil engagement by the row unit necessitates predetermined soil penetration by the disc-opener. Conventional implement-mounting linkage mechanisms do not provide for uniform soil penetration of disc-openers across the length of the ground-tool implement frame.
For example, one conventional method for mounting the frame carrying these ground-tool implements onto the wheeled implement, mentioned above, contemplates using a four-point-hitch parallel-linkage design. When the ground-tool implement is the disc and press wheel assembly (i.e., row unit) mentioned above and when the ground-tool implement frame carries a plurality of row-unit assemblies, for example, the upwardly-acting resistive soil forces (when the frame is lowered to the working position and the wheeled implement pulled across the field by a tractor) can result in each disc-opener penetrating the ground less than the desired depth, or at times can even result in the failure of certain discs to penetrate the ground at all. Because four-point-hitch parallel-linked frames of this sort are connected to wheeled implements, of the type mentioned above, by pivoted members, frames of this sort necessarily include separate wheels mounted thereon for supporting the weight of the frame and the weight of the ground-tool implements (also mounted thereon). The conventional parallel-linked four-point-hitch manner of mounting such wheeled ground-tool frames to the above-mentioned other wheeled farm implement, however, results in there being a moment imposed about the wheeled farm implement axle, due to the overhung load of the row units in relation to the frame onto which the row units are mounted. The imposition of such a moment might be unacceptable to a tractor operator. For example, such a moment can be great enough to cause the tractor-end of the hitch to be lifted off the ground, when the hitch is disconnected from the tractor, resulting in what is known as "negative hitch weight", which is totally unacceptable to most tractor operators.
Because seed-weight is often balanced in a wheeled seed-hopper farm implement of the type mentioned above, seed-weight has virtually no effect in counteracting such a moment. However, seed weight in the wheeled seed hopper does assist in forcing the soil-engaging ground-tool implements into the soil in the dynamic case, as can be determined by performing structural analysis upon the links of the conventional four-point-hitch parallel-link design. However, when the above-mentioned air-seeder distribution system causes the wheeled hopper to become depleted of its seed supply, the seed-assisting force being imposed upon the individual row units is correspondingly diminished.
Thus, conventional four-point-hitch designs cannot reduce or solve the above-discussed problems. Adding counter-balancing weight to counteract the above-discussed moment or to assist in forcing the soil-engaging ground tools into the ground, is not the answer, however, because addition of weight only tends to reduce the tractor operator's acreage-yield to fuel-consumption ratio, as more fuel is required to transport the extra weight through the field. For obvious reasons, this too is unacceptable.